How to Calibrate a Click Torque Wrench
You may find it necessary to calibrate your click torque wrench if you feel it is not tightening properly. This type of wrench is very handy as you can set the appropriate torque and then know that the nut or bolt will be tightened to the correct point. Many times the bolt will need to be a specific tightness to allow for any swelling or shrinking of what it is screwed into.
Step 1. The Square Drive
Make sure you put the square drive into a vise. You only want the square drive to touch the vise and not the body of the wrench. The vise holds the wrench in a horizontal position. First measure out from the center of this square drive to your chosen calibration point. This point would correspond to the center of the fastener to the marking. The center is the point at which the 2 diagonal lines intersect. Write down the number in the units that the wrench is marked in. Normally this will be in foot pounds or in inch pounds.
Step 2. A Weight
You will need a weight which will be used to put some force onto the handle. A 20 or 40 pound weight will work. Now multiply the measured center of the square distance by the weight. If you do not have a weight handy then find something that is heavy enough of which you know the exact weight. Filling a gallon of milk with sand is handy. Just make sure you weigh it first.
Step 3. Set the Wrench
You want to set your wrench to the number you calculated from the weight and center distance. You want to hang the weight from this point or mark on the handle of the wrench. Once the weight is on the wrench it may click. If the wrench clicks then move the weight closer to the handle. Once you have reached a point when it doesn’t click, move it away from the vice until it does click. It can take some time but you want to find the point where when the weight is on, you are at a point between the wrench clicking and not clicking.
Step 4. Calibration Ratio
You want to measure this new distance. This will be the new ratio distance and you can apply a calibration factor if necessary. This ratio will be the first distance you measured divided by the second distance you measured with the weight, D1/D2. Now you can use this ratio to properly use your click wrench.
Step 5. Using the Calibration Ratio
Now each time you use the wrench you will need to use this calibration ratio. So if you need to apply a torque of 50 ft pounds, multiple the 50 ft pounds by your ratio of D1/D2. This will tell you what setting you will need to set your wrench to. If your wrench is off then this setting will not be at the 50 ft pound mark but at a different distance.
Step 6. When to Calibrate
If you use your wrench a lot, then you will want to calibrate it frequently. If not, see about calibrating it every once in a while. If you are using it to tighten something that must be at the correct torque, then you should calibrate the wrench first.